Copper Binding Induces Polymorphism in Amyloid-β Peptide: Results of Computational Models

Amyloid-β (Aβ) peptides are intrinsically disordered peptides, and their aggregation is the hallmark of Alzheimer's disease development. The propensity of the Aβ peptide to intermolecular interactions, the latter favoring different types of oligomers and aggregated forms, has been the object of a huge number of studies. Several facts are now established: the presence of large amount of d-block (M) ions (Zn, Cu, and Fe) in the aggregated forms; the 1:1 M/Aβ ratio favors the formation of amorphous aggregates, with an aggregation rate lower than that in the absence of such ions. In particular, statistical models describing the interactions between copper and amyloid peptides are mandatory to explain the relationship between neurodegeneration, copper dyshomeostasis, and overproduction of reactive oxygen species, the latter event occurring with aging. In this work, we show, by replica-exchange molecular dynamics simulations, that a copper ion (Cu²⁺) bound as in the experimentally observed prevailing coordination enhances the probability of closed structures that hinder the formation of extended intermolecular hydrogen bonds that stabilize fibrillar ordered aggregated forms. On the other hand, this effect enhances the catalytic role of the complex during the lifetime of soluble forms.